1. Field of the Invention
The present invention relates to a method of cleaning a diffusion furnace of semiconductor manufacturing equipment and to an auxiliary cleaner for cleaning the same. More particularly, the present invention relates to a method of and an auxiliary cleaner for cleaning a diffusion furnace of semiconductor manufacturing equipment using CIF3 gas.
2. Description of the Related Art
In general, semiconductor devices are manufactured by selectively and repeatedly performing processes, such as photolithography, etching, diffusion, chemical vapor deposition, ion implantation, and metal deposition processes, on a wafer. The diffusion process is performed frequently among the aforementioned processes to diffuse desired conductive impurities into the wafer.
The diffusion process is performed in a diffusion furnace at a high temperature. In addition, the diffusion furnace may be used to form a thermal oxide layer on a wafer at about 900° C. or higher, to form an SiO2 layer on a wafer using SiH4 gas, to form a thin polysilicon layer on a wafer, and to perform annealing and baking processes, or the like.
In particular, the thin polysilicon layer-forming process is carried out using SiH4+PH3 gas. In this process, material is continuously deposited on interior parts of the diffusion furnace, thereby forming an undesirable membrane on the inside of the furnace. The membrane flakes off of or lifts from the interior parts of the furnace once it attains a certain thickness. As a result, the quality of the thin layer being formed on the surface of the wafer may be diminished.
Therefore, the membrane is periodically removed from the inner parts of the diffusion furnace using ClF3 gas is used. That is, ClF3 gas is injected into the diffusion furnace to remove the deposits from the interior parts of the diffusion furnace.
FIG. 1 schematically illustrates a conventional process of removing a membrane formed in a diffusion furnace. The diffusion furnace 100 includes an outer tube 110 exposed to the ambient outside the furnace, and an inner tube 112 located in the outer tube 110. A supply pipe 114 and a discharge pipe 116 for injecting and discharging ClF3 gas into/from the diffusion furnace 100 are mounted at the lower part of the diffusion furnace 100. In addition, a support plate 118 is disposed at the bottom of the furnace 100 to support a wafer boat 120 in which the wafer is seated.
As shown in FIG. 2, the wafer boat 120 has three annular plates 122a, 122b and 122c supported in parallel by three rods 126 such that a hole 124 extends through the center of the boat 120. The diffusion furnace 100 is cleaned while the boat 120 is disposed in the diffusion furnace 100 in an attempt to direct the injected ClF3 gas toward the inner wall of the inner tube 112 and out of the central region of the furnace.
However, as shown in FIG. 2, the structure of the wafer boat 120 is mostly open to allow the wafer to be loaded onto the boat 120. Accordingly, most of the ClF3 gas passes through the boat 120, especially through the hole 124 defined by the center of the annular plates 122a, 122b and 122c. As a result, the ClF3 gas can remain at the center of the furnace, i.e., the boat 120 does little to induce the ClF3 gas to flow towards the inner wall of the inner tube 112. In addition, the ClF3 gas flows rapidly throughout the interior of the furnace. Accordingly, the furnace is not cleaned efficiently, i.e., a large amount of the ClF3 is consumed during the cleaning process.